httpclient/helpers.go

package httpclient

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"net/http"

	"code.nochebuena.dev/go/xerrors"
)

// DoJSON executes req and decodes the JSON response body into T.
// Returns a xerrors-typed error for HTTP 4xx/5xx responses.
func DoJSON[T any](ctx context.Context, client Client, req *http.Request) (*T, error) {
	req = req.WithContext(ctx)
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 400 {
		return nil, MapStatusToError(resp.StatusCode, "external API error")
	}

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, xerrors.New(xerrors.ErrInternal, "failed to read response body").WithError(err)
	}

	var data T
	if err := json.Unmarshal(body, &data); err != nil {
		return nil, xerrors.New(xerrors.ErrInternal, "failed to decode JSON response").WithError(err)
	}

	return &data, nil
}

// DoJSONRequest serialises body as JSON, POST/PUT/PATCHes it to rawURL, and
// decodes the response into Resp. For requests without a body, use DoJSON instead.
func DoJSONRequest[Req, Resp any](ctx context.Context, client Client, method, rawURL string, body Req) (*Resp, error) {
	data, err := json.Marshal(body)
	if err != nil {
		return nil, xerrors.New(xerrors.ErrInternal, "failed to encode request body").WithError(err)
	}
	req, err := http.NewRequestWithContext(ctx, method, rawURL, bytes.NewReader(data))
	if err != nil {
		return nil, xerrors.New(xerrors.ErrInternal, "failed to create request").WithError(err)
	}
	req.Header.Set("Content-Type", "application/json")
	return DoJSON[Resp](ctx, client, req)
}

// MapStatusToError maps an HTTP status code to the matching xerrors type.
func MapStatusToError(code int, msg string) error {
	switch code {
	case http.StatusNotFound:
		return xerrors.New(xerrors.ErrNotFound, msg)
	case http.StatusBadRequest:
		return xerrors.New(xerrors.ErrInvalidInput, msg)
	case http.StatusUnauthorized:
		return xerrors.New(xerrors.ErrUnauthorized, msg)
	case http.StatusForbidden:
		return xerrors.New(xerrors.ErrPermissionDenied, msg)
	case http.StatusConflict:
		return xerrors.New(xerrors.ErrAlreadyExists, msg)
	case http.StatusTooManyRequests:
		return xerrors.New(xerrors.ErrUnavailable, msg)
	default:
		return xerrors.New(xerrors.ErrInternal, msg)
	}
}